<template>
  <el-breadcrumb class="app-breadcrumb" separator="/">
    <!-- transition-group是表示的一组动画 -->
    <transition-group name="breadcrumb">
      <el-breadcrumb-item v-for="(item, index) in levelList" :key="item.path">
        <span v-if="item.redirect === 'noRedirect' || index == levelList.length - 1" class="no-redirect">{{
          item.meta.title }}</span>
        <a v-else @click.prevent="handleLink(item)">{{ item.meta.title }}</a>
      </el-breadcrumb-item>
    </transition-group>
  </el-breadcrumb>
</template>

<script>
export default {
  data() {
    return {
      levelList: null
    }
  },
  watch: {
    $route(route) {
      // if you go to the redirect page, do not update the breadcrumbs
      if (route.path.startsWith('/redirect/')) {
        return
      }
      this.getBreadcrumb()
    }
  },
  created() {
    this.getBreadcrumb()
  },
  methods: {
    getBreadcrumb() {
      // only show routes with meta.title
      let matched = this.$route.matched.filter(item => item.meta && item.meta.title)
      const first = matched[0]

      //默认为面包屑添加"首页"
      if (!this.isDashboard(first)) {
        //matched拼接成一个面包屑列表
        matched = [{ path: '/index', meta: { title: '首页' } }].concat(matched)
      }

      //levelList:遍历面包屑的对象
      this.levelList = matched.filter(item => item.meta && item.meta.title && item.meta.breadcrumb !== false)
    },
    /**
     * 判断route是否是"首页"
     * @param {*} route 
     */
    isDashboard(route) {
      const name = route && route.name
      if (!name) {
        return false
      }
      return name.trim() === 'Index'
    },

    handleLink(item) {
      const { redirect, path } = item
      //存在指定redirect跳转位置时，则跳转到指定位置，否则跳转到path路径
      if (redirect) {
        this.$router.push(redirect)
        return
      }
      this.$router.push(path)
    }
  }
}
</script>

<style lang="scss" scoped>
.app-breadcrumb.el-breadcrumb {
  display: inline-block;
  font-size: 14px;
  line-height: 50px;
  margin-left: 8px;

  .no-redirect {
    color: #97a8be;
    cursor: text;
  }
}
</style>
